[docs]defAZ(s=None):"""Return the letters of ``s`` in uppercase. In case more than one string is passed, each of them will be processed and a list of upper case strings will be returned. Examples ======== >>> from sympy.crypto.crypto import AZ >>> AZ('Hello, world!') 'HELLOWORLD' >>> AZ('Hello, world!'.split()) ['HELLO', 'WORLD'] See Also ======== check_and_join """ifnots:returnuppercaset=type(s)isstrift:s=[s]rv=[check_and_join(i.upper().split(),uppercase,filter=True)foriins]ift:returnrv[0]returnrv

bifid5=AZ().replace('J','')bifid6=AZ()+'0123456789'bifid10=printable

[docs]defpadded_key(key,symbols,filter=True):"""Return a string of the distinct characters of ``symbols`` with those of ``key`` appearing first, omitting characters in ``key`` that are not in ``symbols``. A ValueError is raised if a) there are duplicate characters in ``symbols`` or b) there are characters in ``key`` that are not in ``symbols``. Examples ======== >>> from sympy.crypto.crypto import padded_key >>> padded_key('PUPPY', 'OPQRSTUVWXY') 'PUYOQRSTVWX' >>> padded_key('RSA', 'ARTIST') Traceback (most recent call last): ... ValueError: duplicate characters in symbols: T """syms=list(uniq(symbols))iflen(syms)!=len(symbols):extra=''.join(sorted(set([iforiinsymbolsifsymbols.count(i)>1])))raiseValueError('duplicate characters in symbols: %s'%extra)extra=set(key)-set(syms)ifextra:raiseValueError('characters in key but not symbols: %s'%''.join(sorted(extra)))key0=''.join(list(uniq(key)))returnkey0+''.join([iforiinsymsifinotinkey0])

[docs]defcheck_and_join(phrase,symbols=None,filter=None):""" Joins characters of `phrase` and if ``symbols`` is given, raises an error if any character in ``phrase`` is not in ``symbols``. Parameters ========== phrase: string or list of strings to be returned as a string symbols: iterable of characters allowed in ``phrase``; if ``symbols`` is None, no checking is performed Examples ======== >>> from sympy.crypto.crypto import check_and_join >>> check_and_join('a phrase') 'a phrase' >>> check_and_join('a phrase'.upper().split()) 'APHRASE' >>> check_and_join('a phrase!'.upper().split(), 'ARE', filter=True) 'ARAE' >>> check_and_join('a phrase!'.upper().split(), 'ARE') Traceback (most recent call last): ... ValueError: characters in phrase but not symbols: "!HPS" """rv=''.join(''.join(phrase))ifsymbolsisnotNone:symbols=check_and_join(symbols)missing=''.join(list(sorted(set(rv)-set(symbols))))ifmissing:ifnotfilter:raiseValueError('characters in phrase but not symbols: "%s"'%missing)rv=translate(rv,None,missing)returnrv

[docs]defencipher_shift(msg,key,symbols=None):""" Performs shift cipher encryption on plaintext msg, and returns the ciphertext. Notes ===== The shift cipher is also called the Caesar cipher, after Julius Caesar, who, according to Suetonius, used it with a shift of three to protect messages of military significance. Caesar's nephew Augustus reportedly used a similar cipher, but with a right shift of 1. ALGORITHM: INPUT: ``key``: an integer (the secret key) ``msg``: plaintext of upper-case letters OUTPUT: ``ct``: ciphertext of upper-case letters STEPS: 0. Number the letters of the alphabet from 0, ..., N 1. Compute from the string ``msg`` a list ``L1`` of corresponding integers. 2. Compute from the list ``L1`` a new list ``L2``, given by adding ``(k mod 26)`` to each element in ``L1``. 3. Compute from the list ``L2`` a string ``ct`` of corresponding letters. Examples ======== >>> from sympy.crypto.crypto import encipher_shift, decipher_shift >>> msg = "GONAVYBEATARMY" >>> ct = encipher_shift(msg, 1); ct 'HPOBWZCFBUBSNZ' To decipher the shifted text, change the sign of the key: >>> encipher_shift(ct, -1) 'GONAVYBEATARMY' There is also a convenience function that does this with the original key: >>> decipher_shift(ct, 1) 'GONAVYBEATARMY' """msg,_,A=_prep(msg,'',symbols)shift=len(A)-key%len(A)key=A[shift:]+A[:shift]returntranslate(msg,key,A)

[docs]defdecipher_shift(msg,key,symbols=None):""" Return the text by shifting the characters of ``msg`` to the left by the amount given by ``key``. Examples ======== >>> from sympy.crypto.crypto import encipher_shift, decipher_shift >>> msg = "GONAVYBEATARMY" >>> ct = encipher_shift(msg, 1); ct 'HPOBWZCFBUBSNZ' To decipher the shifted text, change the sign of the key: >>> encipher_shift(ct, -1) 'GONAVYBEATARMY' Or use this function with the original key: >>> decipher_shift(ct, 1) 'GONAVYBEATARMY' """returnencipher_shift(msg,-key,symbols)######## affine cipher examples ############

[docs]defencipher_affine(msg,key,symbols=None,_inverse=False):r""" Performs the affine cipher encryption on plaintext ``msg``, and returns the ciphertext. Encryption is based on the map `x \rightarrow ax+b` (mod `N`) where ``N`` is the number of characters in the alphabet. Decryption is based on the map `x \rightarrow cx+d` (mod `N`), where `c = a^{-1}` (mod `N`) and `d = -a^{-1}b` (mod `N`). In particular, for the map to be invertible, we need `\mathrm{gcd}(a, N) = 1` and an error will be raised if this is not true. Notes ===== This is a straightforward generalization of the shift cipher with the added complexity of requiring 2 characters to be deciphered in order to recover the key. ALGORITHM: INPUT: ``msg``: string of characters that appear in ``symbols`` ``a, b``: a pair integers, with ``gcd(a, N) = 1`` (the secret key) ``symbols``: string of characters (default = uppercase letters). When no symbols are given, ``msg`` is converted to upper case letters and all other charactes are ignored. OUTPUT: ``ct``: string of characters (the ciphertext message) STEPS: 0. Number the letters of the alphabet from 0, ..., N 1. Compute from the string ``msg`` a list ``L1`` of corresponding integers. 2. Compute from the list ``L1`` a new list ``L2``, given by replacing ``x`` by ``a*x + b (mod N)``, for each element ``x`` in ``L1``. 3. Compute from the list ``L2`` a string ``ct`` of corresponding letters. See Also ======== decipher_affine """msg,_,A=_prep(msg,'',symbols)N=len(A)a,b=keyassertgcd(a,N)==1if_inverse:c=mod_inverse(a,N)d=-b*ca,b=c,dB=''.join([A[(a*i+b)%N]foriinrange(N)])returntranslate(msg,A,B)

[docs]defencipher_substitution(msg,old,new=None):""" Returns the ciphertext obtained by replacing each character that appears in ``old`` with the corresponding character in ``new``. If ``old`` is a mapping, then new is ignored and the replacements defined by ``old`` are used. Notes ===== This is a more general than the affine cipher in that the key can only be recovered by determining the mapping for each symbol. Though in practice, once a few symbols are recognized the mappings for other characters can be quickly guessed. Examples ======== >>> from sympy.crypto.crypto import encipher_substitution, AZ >>> old = 'OEYAG' >>> new = '034^6' >>> msg = AZ("go navy! beat army!") >>> ct = encipher_substitution(msg, old, new); ct '60N^V4B3^T^RM4' To decrypt a substitution, reverse the last two arguments: >>> encipher_substitution(ct, new, old) 'GONAVYBEATARMY' In the special case where ``old`` and ``new`` are a permuation of order 2 (representing a transposition of characters) their order is immaterial: >>> old = 'NAVY' >>> new = 'ANYV' >>> encipher = lambda x: encipher_substitution(x, old, new) >>> encipher('NAVY') 'ANYV' >>> encipher(_) 'NAVY' The substitution cipher, in general, is a method whereby "units" (not necessarily single characters) of plaintext are replaced with ciphertext according to a regular system. >>> ords = dict(zip('abc', ['\\%i' % ord(i) for i in 'abc'])) >>> print(encipher_substitution('abc', ords)) \97\98\99 """returntranslate(msg,old,new)########################################################################################## Vigenère cipher examples ##############################################################################################

[docs]defencipher_vigenere(msg,key,symbols=None):""" Performs the Vigenère cipher encryption on plaintext ``msg``, and returns the ciphertext. Examples ======== >>> from sympy.crypto.crypto import encipher_vigenere, AZ >>> key = "encrypt" >>> msg = "meet me on monday" >>> encipher_vigenere(msg, key) 'QRGKKTHRZQEBPR' Section 1 of the Kryptos sculpture at the CIA headquarters uses this cipher and also changes the order of the the alphabet [2]_. Here is the first line of that section of the sculpture: >>> from sympy.crypto.crypto import decipher_vigenere, padded_key >>> alp = padded_key('KRYPTOS', AZ()) >>> key = 'PALIMPSEST' >>> msg = 'EMUFPHZLRFAXYUSDJKZLDKRNSHGNFIVJ' >>> decipher_vigenere(msg, key, alp) 'BETWEENSUBTLESHADINGANDTHEABSENC' Notes ===== The Vigenère cipher is named after Blaise de Vigenère, a sixteenth century diplomat and cryptographer, by a historical accident. Vigenère actually invented a different and more complicated cipher. The so-called *Vigenère cipher* was actually invented by Giovan Batista Belaso in 1553. This cipher was used in the 1800's, for example, during the American Civil War. The Confederacy used a brass cipher disk to implement the Vigenère cipher (now on display in the NSA Museum in Fort Meade) [1]_. The Vigenère cipher is a generalization of the shift cipher. Whereas the shift cipher shifts each letter by the same amount (that amount being the key of the shift cipher) the Vigenère cipher shifts a letter by an amount determined by the key (which is a word or phrase known only to the sender and receiver). For example, if the key was a single letter, such as "C", then the so-called Vigenere cipher is actually a shift cipher with a shift of `2` (since "C" is the 2nd letter of the alphabet, if you start counting at `0`). If the key was a word with two letters, such as "CA", then the so-called Vigenère cipher will shift letters in even positions by `2` and letters in odd positions are left alone (shifted by `0`, since "A" is the 0th letter, if you start counting at `0`). ALGORITHM: INPUT: ``msg``: string of characters that appear in ``symbols`` (the plaintext) ``key``: a string of characters that appear in ``symbols`` (the secret key) ``symbols``: a string of letters defining the alphabet OUTPUT: ``ct``: string of characters (the ciphertext message) STEPS: 0. Number the letters of the alphabet from 0, ..., N 1. Compute from the string ``key`` a list ``L1`` of corresponding integers. Let ``n1 = len(L1)``. 2. Compute from the string ``msg`` a list ``L2`` of corresponding integers. Let ``n2 = len(L2)``. 3. Break ``L2`` up sequencially into sublists of size ``n1``; the last sublist may be smaller than ``n1`` 4. For each of these sublists ``L`` of ``L2``, compute a new list ``C`` given by ``C[i] = L[i] + L1[i] (mod N)`` to the ``i``-th element in the sublist, for each ``i``. 5. Assemble these lists ``C`` by concatenation into a new list of length ``n2``. 6. Compute from the new list a string ``ct`` of corresponding letters. Once it is known that the key is, say, `n` characters long, frequency analysis can be applied to every `n`-th letter of the ciphertext to determine the plaintext. This method is called *Kasiski examination* (although it was first discovered by Babbage). If they key is as long as the message and is comprised of randomly selected characters -- a one-time pad -- the message is theoretically unbreakable. The cipher Vigenère actually discovered is an "auto-key" cipher described as follows. ALGORITHM: INPUT: ``key``: a string of letters (the secret key) ``msg``: string of letters (the plaintext message) OUTPUT: ``ct``: string of upper-case letters (the ciphertext message) STEPS: 0. Number the letters of the alphabet from 0, ..., N 1. Compute from the string ``msg`` a list ``L2`` of corresponding integers. Let ``n2 = len(L2)``. 2. Let ``n1`` be the length of the key. Append to the string ``key`` the first ``n2 - n1`` characters of the plaintext message. Compute from this string (also of length ``n2``) a list ``L1`` of integers corresponding to the letter numbers in the first step. 3. Compute a new list ``C`` given by ``C[i] = L1[i] + L2[i] (mod N)``. 4. Compute from the new list a string ``ct`` of letters corresponding to the new integers. To decipher the auto-key ciphertext, the key is used to decipher the first ``n1`` characters and then those characters become the key to decipher the next ``n1`` characters, etc...: >>> m = AZ('go navy, beat army! yes you can'); m 'GONAVYBEATARMYYESYOUCAN' >>> key = AZ('gold bug'); n1 = len(key); n2 = len(m) >>> auto_key = key + m[:n2 - n1]; auto_key 'GOLDBUGGONAVYBEATARMYYE' >>> ct = encipher_vigenere(m, auto_key); ct 'MCYDWSHKOGAMKZCELYFGAYR' >>> n1 = len(key) >>> pt = [] >>> while ct: ... part, ct = ct[:n1], ct[n1:] ... pt.append(decipher_vigenere(part, key)) ... key = pt[-1] ... >>> ''.join(pt) == m True References ========== .. [1] http://en.wikipedia.org/wiki/Vigenere_cipher .. [2] http://web.archive.org/web/20071116100808/ http://filebox.vt.edu/users/batman/kryptos.html """msg,key,A=_prep(msg,key,symbols)map=dict([(c,i)fori,cinenumerate(A)])key=[map[c]forcinkey]N=len(map)k=len(key)rv=[]fori,minenumerate(msg):rv.append(A[(map[m]+key[i%k])%N])rv=''.join(rv)returnrv

[docs]defencipher_hill(msg,key,symbols=None,pad="Q"):r""" Return the Hill cipher encryption of ``msg``. Notes ===== The Hill cipher [1]_, invented by Lester S. Hill in the 1920's [2]_, was the first polygraphic cipher in which it was practical (though barely) to operate on more than three symbols at once. The following discussion assumes an elementary knowledge of matrices. First, each letter is first encoded as a number starting with 0. Suppose your message `msg` consists of `n` capital letters, with no spaces. This may be regarded an `n`-tuple M of elements of `Z_{26}` (if the letters are those of the English alphabet). A key in the Hill cipher is a `k x k` matrix `K`, all of whose entries are in `Z_{26}`, such that the matrix `K` is invertible (i.e., the linear transformation `K: Z_{N}^k \rightarrow Z_{N}^k` is one-to-one). ALGORITHM: INPUT: ``msg``: plaintext message of `n` upper-case letters ``key``: a `k x k` invertible matrix `K`, all of whose entries are in `Z_{26}` (or whatever number of symbols are being used). ``pad``: character (default "Q") to use to make length of text be a multiple of ``k`` OUTPUT: ``ct``: ciphertext of upper-case letters STEPS: 0. Number the letters of the alphabet from 0, ..., N 1. Compute from the string ``msg`` a list ``L`` of corresponding integers. Let ``n = len(L)``. 2. Break the list ``L`` up into ``t = ceiling(n/k)`` sublists ``L_1``, ..., ``L_t`` of size ``k`` (with the last list "padded" to ensure its size is ``k``). 3. Compute new list ``C_1``, ..., ``C_t`` given by ``C[i] = K*L_i`` (arithmetic is done mod N), for each ``i``. 4. Concatenate these into a list ``C = C_1 + ... + C_t``. 5. Compute from ``C`` a string ``ct`` of corresponding letters. This has length ``k*t``. References ========== .. [1] en.wikipedia.org/wiki/Hill_cipher .. [2] Lester S. Hill, Cryptography in an Algebraic Alphabet, The American Mathematical Monthly Vol.36, June-July 1929, pp.306-312. See Also ======== decipher_hill """assertkey.is_squareassertlen(pad)==1msg,pad,A=_prep(msg,pad,symbols)map=dict([(c,i)fori,cinenumerate(A)])P=[map[c]forcinmsg]N=len(A)k=key.colsn=len(P)m,r=divmod(n,k)ifr:P=P+[map[pad]]*(k-r)m+=1rv=''.join([A[c%N]forjinrange(m)forcinlist(key*Matrix(k,1,[P[i]foriinrange(k*j,k*(j+1))]))])returnrv

[docs]defdecipher_hill(msg,key,symbols=None):""" Deciphering is the same as enciphering but using the inverse of the key matrix. Examples ======== >>> from sympy.crypto.crypto import encipher_hill, decipher_hill >>> from sympy import Matrix >>> key = Matrix([[1, 2], [3, 5]]) >>> encipher_hill("meet me on monday", key) 'UEQDUEODOCTCWQ' >>> decipher_hill(_, key) 'MEETMEONMONDAY' When the length of the plaintext (stripped of invalid characters) is not a multiple of the key dimension, extra characters will appear at the end of the enciphered and deciphered text. In order to decipher the text, those characters must be included in the text to be deciphered. In the following, the key has a dimension of 4 but the text is 2 short of being a multiple of 4 so two characters will be added. >>> key = Matrix([[1, 1, 1, 2], [0, 1, 1, 0], ... [2, 2, 3, 4], [1, 1, 0, 1]]) >>> msg = "ST" >>> encipher_hill(msg, key) 'HJEB' >>> decipher_hill(_, key) 'STQQ' >>> encipher_hill(msg, key, pad="Z") 'ISPK' >>> decipher_hill(_, key) 'STZZ' If the last two characters of the ciphertext were ignored in either case, the wrong plaintext would be recovered: >>> decipher_hill("HD", key) 'ORMV' >>> decipher_hill("IS", key) 'UIKY' """assertkey.is_squaremsg,_,A=_prep(msg,'',symbols)map=dict([(c,i)fori,cinenumerate(A)])C=[map[c]forcinmsg]N=len(A)k=key.colsn=len(C)m,r=divmod(n,k)ifr:C=C+[0]*(k-r)m+=1key_inv=key.inv_mod(N)rv=''.join([A[p%N]forjinrange(m)forpinlist(key_inv*Matrix(k,1,[C[i]foriinrange(k*j,k*(j+1))]))])returnrv#################### Bifid cipher ########################

[docs]defencipher_bifid(msg,key,symbols=None):r""" Performs the Bifid cipher encryption on plaintext ``msg``, and returns the ciphertext. This is the version of the Bifid cipher that uses an `n \times n` Polybius square. INPUT: ``msg``: plaintext string ``key``: short string for key; duplicate characters are ignored and then it is padded with the characters in ``symbols`` that were not in the short key ``symbols``: `n \times n` characters defining the alphabet (default is string.printable) OUTPUT: ciphertext (using Bifid5 cipher without spaces) See Also ======== decipher_bifid, encipher_bifid5, encipher_bifid6 """msg,key,A=_prep(msg,key,symbols,bifid10)long_key=''.join(uniq(key))orAn=len(A)**.5ifn!=int(n):raiseValueError('Length of alphabet (%s) is not a square number.'%len(A))N=int(n)iflen(long_key)<N**2:long_key=list(long_key)+[xforxinAifxnotinlong_key]# the fractionalizationrow_col=dict([(ch,divmod(i,N))fori,chinenumerate(long_key)])r,c=zip(*[row_col[x]forxinmsg])rc=r+cch=dict([(i,ch)forch,iinrow_col.items()])rv=''.join((ch[i]foriinzip(rc[::2],rc[1::2])))returnrv

[docs]defdecipher_bifid(msg,key,symbols=None):r""" Performs the Bifid cipher decryption on ciphertext ``msg``, and returns the plaintext. This is the version of the Bifid cipher that uses the `n \times n` Polybius square. INPUT: ``msg``: ciphertext string ``key``: short string for key; duplicate characters are ignored and then it is padded with the characters in ``symbols`` that were not in the short key ``symbols``: `n \times n` characters defining the alphabet (default=string.printable, a `10 \times 10` matrix) OUTPUT: deciphered text Examples ======== >>> from sympy.crypto.crypto import ( ... encipher_bifid, decipher_bifid, AZ) Do an encryption using the bifid5 alphabet: >>> alp = AZ().replace('J', '') >>> ct = AZ("meet me on monday!") >>> key = AZ("gold bug") >>> encipher_bifid(ct, key, alp) 'IEILHHFSTSFQYE' When entering the text or ciphertext, spaces are ignored so it can be formatted as desired. Re-entering the ciphertext from the preceding, putting 4 characters per line and padding with an extra J, does not cause problems for the deciphering: >>> decipher_bifid(''' ... IEILH ... HFSTS ... FQYEJ''', key, alp) 'MEETMEONMONDAY' When no alphabet is given, all 100 printable characters will be used: >>> key = '' >>> encipher_bifid('hello world!', key) 'bmtwmg-bIo*w' >>> decipher_bifid(_, key) 'hello world!' If the key is changed, a different encryption is obtained: >>> key = 'gold bug' >>> encipher_bifid('hello world!', 'gold_bug') 'hg2sfuei7t}w' And if the key used to decrypt the message is not exact, the original text will not be perfectly obtained: >>> decipher_bifid(_, 'gold pug') 'heldo~wor6d!' """msg,_,A=_prep(msg,'',symbols,bifid10)long_key=''.join(uniq(key))orAn=len(A)**.5ifn!=int(n):raiseValueError('Length of alphabet (%s) is not a square number.'%len(A))N=int(n)iflen(long_key)<N**2:long_key=list(long_key)+[xforxinAifxnotinlong_key]# the reverse fractionalizationrow_col=dict([(ch,divmod(i,N))fori,chinenumerate(long_key)])rc=[iforcinmsgforiinrow_col[c]]n=len(msg)rc=zip(*(rc[:n],rc[n:]))ch=dict([(i,ch)forch,iinrow_col.items()])rv=''.join((ch[i]foriinrc))returnrv

[docs]defencipher_bifid5(msg,key):r""" Performs the Bifid cipher encryption on plaintext ``msg``, and returns the ciphertext. This is the version of the Bifid cipher that uses the `5 \times 5` Polybius square. The letter "J" is ignored so it must be replaced with something else (traditionally an "I") before encryption. Notes ===== The Bifid cipher was invented around 1901 by Felix Delastelle. It is a *fractional substitution* cipher, where letters are replaced by pairs of symbols from a smaller alphabet. The cipher uses a `5 \times 5` square filled with some ordering of the alphabet, except that "J" is replaced with "I" (this is a so-called Polybius square; there is a `6 \times 6` analog if you add back in "J" and also append onto the usual 26 letter alphabet, the digits 0, 1, ..., 9). According to Helen Gaines' book *Cryptanalysis*, this type of cipher was used in the field by the German Army during World War I. ALGORITHM: (5x5 case) INPUT: ``msg``: plaintext string; converted to upper case and filtered of anything but all letters except J. ``key``: short string for key; non-alphabetic letters, J and duplicated characters are ignored and then, if the length is less than 25 characters, it is padded with other letters of the alphabet (in alphabetical order). OUTPUT: ciphertext (all caps, no spaces) STEPS: 0. Create the `5 \times 5` Polybius square ``S`` associated to ``key`` as follows: a) moving from left-to-right, top-to-bottom, place the letters of the key into a `5 \times 5` matrix, b) if the key has less than 25 letters, add the letters of the alphabet not in the key until the `5 \times 5` square is filled. 1. Create a list ``P`` of pairs of numbers which are the coordinates in the Polybius square of the letters in ``msg``. 2. Let ``L1`` be the list of all first coordinates of ``P`` (length of ``L1 = n``), let ``L2`` be the list of all second coordinates of ``P`` (so the length of ``L2`` is also ``n``). 3. Let ``L`` be the concatenation of ``L1`` and ``L2`` (length ``L = 2*n``), except that consecutive numbers are paired ``(L[2*i], L[2*i + 1])``. You can regard ``L`` as a list of pairs of length ``n``. 4. Let ``C`` be the list of all letters which are of the form ``S[i, j]``, for all ``(i, j)`` in ``L``. As a string, this is the ciphertext of ``msg``. Examples ======== >>> from sympy.crypto.crypto import ( ... encipher_bifid5, decipher_bifid5) "J" will be omitted unless it is replaced with somthing else: >>> round_trip = lambda m, k: \ ... decipher_bifid5(encipher_bifid5(m, k), k) >>> key = 'a' >>> msg = "JOSIE" >>> round_trip(msg, key) 'OSIE' >>> round_trip(msg.replace("J", "I"), key) 'IOSIE' >>> j = "QIQ" >>> round_trip(msg.replace("J", j), key).replace(j, "J") 'JOSIE' See Also ======== decipher_bifid5, encipher_bifid """msg,key,_=_prep(msg.upper(),key.upper(),None,bifid5)key=padded_key(key,bifid5)returnencipher_bifid(msg,'',key)

[docs]defdecipher_bifid5(msg,key):r""" Return the Bifid cipher decryption of ``msg``. This is the version of the Bifid cipher that uses the `5 \times 5` Polybius square; the letter "J" is ignored unless a ``key`` of length 25 is used. INPUT: ``msg``: ciphertext string ``key``: short string for key; duplicated characters are ignored and if the length is less then 25 characters, it will be padded with other letters from the alphabet omitting "J". Non-alphabetic characters are ignored. OUTPUT: plaintext from Bifid5 cipher (all caps, no spaces) Examples ======== >>> from sympy.crypto.crypto import encipher_bifid5, decipher_bifid5 >>> key = "gold bug" >>> encipher_bifid5('meet me on friday', key) 'IEILEHFSTSFXEE' >>> encipher_bifid5('meet me on monday', key) 'IEILHHFSTSFQYE' >>> decipher_bifid5(_, key) 'MEETMEONMONDAY' """msg,key,_=_prep(msg.upper(),key.upper(),None,bifid5)key=padded_key(key,bifid5)returndecipher_bifid(msg,'',key)

[docs]defencipher_bifid6(msg,key):r""" Performs the Bifid cipher encryption on plaintext ``msg``, and returns the ciphertext. This is the version of the Bifid cipher that uses the `6 \times 6` Polybius square. INPUT: ``msg``: plaintext string (digits okay) ``key``: short string for key (digits okay). If ``key`` is less than 36 characters long, the square will be filled with letters A through Z and digits 0 through 9. OUTPUT: ciphertext from Bifid cipher (all caps, no spaces) See Also ======== decipher_bifid6, encipher_bifid """msg,key,_=_prep(msg.upper(),key.upper(),None,bifid6)key=padded_key(key,bifid6)returnencipher_bifid(msg,'',key)

[docs]defdecipher_bifid6(msg,key):r""" Performs the Bifid cipher decryption on ciphertext ``msg``, and returns the plaintext. This is the version of the Bifid cipher that uses the `6 \times 6` Polybius square. INPUT: ``msg``: ciphertext string (digits okay); converted to upper case ``key``: short string for key (digits okay). If ``key`` is less than 36 characters long, the square will be filled with letters A through Z and digits 0 through 9. All letters are converted to uppercase. OUTPUT: plaintext from Bifid cipher (all caps, no spaces) Examples ======== >>> from sympy.crypto.crypto import encipher_bifid6, decipher_bifid6 >>> key = "gold bug" >>> encipher_bifid6('meet me on monday at 8am', key) 'KFKLJJHF5MMMKTFRGPL' >>> decipher_bifid6(_, key) 'MEETMEONMONDAYAT8AM' """msg,key,_=_prep(msg.upper(),key.upper(),None,bifid6)key=padded_key(key,bifid6)returndecipher_bifid(msg,'',key)